Some lamps having good energy efficiency, such as low pressure discharge lamps (e.g., fluorescent lamps) are generally known. In such lamps, a phosphor layer is employed to convert UV radiation to visible light. For good color properties of the visible light, one or more rare earth-activated phosphors are commonly employed in the layer. However, recent trends have increased the cost of rare earth-activated phosphors. This has given rise to a need to improve the lumen performance of fluorescent lamps with respect to the amount of phosphor coating used in the lamp.
In some known fluorescent lamps, relatively coarse rare earth phosphor particle systems have been used to achieve higher lumens. However, in so doing, the use of more phosphor (i.e., high coating weights) is required to achieve a thick enough layer of phosphor coating to absorb all the available ultraviolet light energy.
Therefore, in consideration of a cost increase in rare earth materials such as europium-activated yttrium oxide red phosphor, cerium- and terbium-activated green phosphor, europium-activated blue phosphors, and other phosphors that use rare earths, there is a need to avoid high coating weights in lamps.